it's very suspicious about a price, even with 107,000 miles. Those cars (2007) is worth about 20,000 with even the mileage. About valve seats it's not many cases, remember it's a forum and people attend to report a problem, and also I saw about two occasions with this problem for last couple years on 550i and now assume how many 550 were sold, let's assume 10% didn't report as they don't care and another 90% are still good cars. This problem could be due oil, overheating, manufacture defects, putting a wrong oil additives and many other factors. Also this problem could be due people are driving like grandmom and/or short distance, so the carbon build up on valve seats. I talked to BMW and they suggested this car should drive hard at least once a week.
I have 86000 miles and I don't have oil consumption at all (knock on wood) even with aggressive driving.